This invention relates to masonry wall construction, and is more particularly directed to a process of creating a wall or similar structure of masonry units which has an increased tensile strength and is able to better withstand environmental stresses such as wind and/or thermal stress loading. In particular, the invention concerns a masonry system in which the bricks, concrete blocks, cinder blocks, stones, or other masonry units are bonded together using an amine-based polymeric foam, such as a water-activated urethane (e.g., single component polyurethane) rather than conventional mortar. An example is a product from Dow Corporation, namely an insulating foam sold under the trademark “Great Stuff”.
Masonry walls are typically erected using masonry blocks or bricks, arranged in linear courses, and a portland-cement based mortar is used as a bonding agent between the masonry blocks of each course. Mortar is also used between successive courses. Mortar, typically composed of portland cement, lime, and sand, has been preferred because of its superior strength under compression. However, mortar has almost no tensile strength, and additional measures, i.e., pre-stressing techniques, have to be taken to account for the tension forces that occur due to wind loading and other factors.
Masonry walls, e.g., walls formed by stacking concrete blocks, are a common construction method. Such walls have high compression strength but very little tensile strength. As a consequence, it is common to shore concrete block walls during construction, at least until the roof trusses and roof are in place, so that wind does not blow them over. The additional structure is necessary to provide lateral support and to add weight, loading the wall compressively. In high wind areas, i.e., hurricane zones, it is common to require that the top plate of the wall be through-bolted to the foundation slab, so that there is always a net compressive force on the wall. Conventional concrete block walls also experience problems that arise from the extreme rigidity of the conventional concrete-mortar bond. When subjected to minor earth movement or to excessive temperature differentials across the wall, there is a tendency for the wall to relieve stress by cracking along the mortar joints. This produces the familiar stair-step crack. These stresses can lead to spalling and other surface damages, as well as deep cracks that affect the integrity of the masonry structure.
Wind has two effects on a masonry building: side wall pressure and aerodynamic lift of the roof. These can add so that the load on the wall becomes negative, with a result of building collapse. In high wind areas, draw bolts run vertically from the plate (on top of the wall) to the foundation. These bolts have to be tightened so as to load the wall compressively above the normal load of the building, so that there is a positive load on the wall for most wind conditions.
Composite wall structures have been proposed in which building blocks such as concrete blocks, are stacked to form a wall, and a polyurethane foam is applied to fill the hollows of the blocks and the spaces within the blocks. The previous use of polyurethane foam simply formed a mechanical bond with the surface structure of the masonry material. One proposed composite wall structure is discussed in U.S. Pat. No. 4,315,391 to Piazza. Another composite wall system is discussed in U.S. Pat. No. 3,653,170 to Sheckler. The Sheckler insulated masonry block design is an appropriate highly energy-efficient and low permeability alternative to the conventional masonry block, and can be constructed in the same dimensions, e.g., 8×8×16 inches.
The use of a two-component polyurethane adhesive in masonry work is discussed, for example, in U.S. Pat. No. 5,951,796 to Murray, U.S. Pat. No. 5,362,342 to Murray et al., and U.S. Pat. No. 6,164,021 to Huber et al. This prior art advocates for two-component polyurethane systems, i.e., those which require an isocyanate component and a polyol component to be blended immediately before application. The prior art avoids the use of moisture-cured single component urethane systems because of perceived disadvantages of slow set time, slow cure rate, high cost per unit weight, and limited shelf life. The prior art entirely misses advantages that the inventor has discovered that arise from chemistry of the urethane formation. That is, the prior art does not recognize the tendency of the amines in the urethane material to bond with the aluminum oxide in the masonry units, and does not recognize that the single component material will have a tendency to strip the water molecules away from the aluminum oxide molecules so that this bonding can take place strongly. The alumina-amide bond strength can be 500% the tensile strength of the urethane material, but this has not been recognized in the masonry arts.